Preterm infants, particularly those of very low birth weight that were born between week 23 and week 28 of gestation, suffer from a very high incidence of respiratory distress syndrome (RDS) related to pulmonary immaturity and inability to make pulmonary surfactant lipids and proteins. These infants are supported by the use of oxygen, ventilators, and routine administration of surfactant replacement. The surfactant replacement preparations currently at use contain surfactant protein (SP) B and SPC but do not contain SPA, SPD, or other innate host-defense proteins (Ikegami et al. 2006; WO 90/11768). SPD is a hydrophilic surfactant protein that decreases pulmonary inflammation and facilitates normal surfactant lipid structure and recycling. Its use as a surfactant replacement has been described (Ikegami et al. 2006; WO 07/056195; WO 02/17878; WO 00/023569; US 2011/0189104; U.S. Pat. No. 7,266,403) but never implemented commercially, possibly due to problems associated with consistent delivery of large oligomerised proteins such as SPD. Furthermore, since repeated intubation or instillation into the airway is challenging in small infants, a sustained release vehicle that provides surfactant replacement, including SPD, for long periods of time in lungs of preterm infants would be highly desirable, but there is currently no system or device for sustained release of SPD in the alveoli of infants or adults.